Structure of a zoom lens barrel

ABSTRACT

A zoom lens barrel includes a cam ring which is driven to rotate; a first lens frame which is positioned around the cam ring, supports a frontmost lens group of a zoom lens system, and includes a first cam follower; a light-shield exterior ring positioned around the first lens frame, and includes a second cam follower; and first and second outer cam grooves formed on an outer peripheral surface of the cam ring so that the first and second cam followers are engaged in the first and second outer cam grooves, respectively. The second cam follower is engaged in the second outer cam groove through a linear guide slot formed on the first lens frame. Zooming ranges of the first and second outer cam grooves are shaped so as to move the first lens frame and the light-shield exterior ring in the same moving path.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a structure of a zoom lensbarrel, and more specifically relates to a structure of a zoom lensbarrel for moving a first lens frame along an optical axis by rotationof a cam ring which is driven to rotate, wherein the first lens framesupports the frontmost lens group among a plurality of lens groups ofthe zoom lens barrel.

[0003] 2. Description of the Related Art

[0004] In conventional zoom lens barrels, it is often the case that afirst lens frame which supports the first lens group (frontmost lensgroup) among a plurality of lens groups of the zoom lens barrel is movedalong an optical axis by rotation of a cam ring which is driven torotate. In the case where a zooming adjustment (which is an adjustmentoperation that is carried out in a manufacturing process of the zoomlens barrel as needed) is carried out by moving the second lens grouppositioned behind the first lens group relative to the first lens group,it is generally the case that an opening for this zooming adjustment isformed on the first lens frame while an independent light-shieldexterior ring is fitted on the first lens frame to cover the opening ina light-tight fashion. This light-shield exterior ring is simply fixedto the first lens frame in conventional zoom lens barrels.

SUMMARY OF THE INVENTION

[0005] The present invention provides an improved structure of a zoomlens barrel for moving the first lens frame along an optical axis byrotation of a cam ring which is driven to rotate, wherein the structureprovides a light-shield exterior ring so as to be multi-functional.

[0006] According to an aspect of the present invention, a zoom lensbarrel is provided, including a cam ring which is driven to rotate; afirst lens frame which is positioned around the cam ring to be guidedlinearly along an optical axis, the first lens frame supporting afrontmost lens group of a zoom lens system; a light-shield exterior ringwhich is positioned around the first lens frame; a first outer camgroove and a second outer cam groove which are formed on an outerperipheral surface of the cam ring, each the first and second camgrooves including a zooming range for performing a zooming operation ofthe zoom lens system; and a first cam follower formed on the first lensframe, the first cam follower being engaged in the first outer camgroove; a second cam follower formed on the light-shield exterior ring,the second cam follower being engaged in the second outer cam groovethrough a linear guide slot which is elongated in a direction parallelto the optical axis, which is formed on the first lens frame. The firstouter cam groove and the second outer cam groove are shaped so as tomove the first lens frame and the light-shield exterior ring in the samemoving path in the zooming ranges thereof.

[0007] It is desirable for the zoom lens barrel to include a lensbarrier unit including at least one barrier blade, wherein the lensbarrier unit is supported by the light-shield exterior ring at a frontend thereof, and retracting ranges of the first outer cam groove and thesecond outer cam groove are shaped so that the light-shield exteriorring advances from a photographing position thereof relative to thefirst lens frame to position the lens barrier unit in front of thefrontmost lens group without the lens barrier unit interfering with thefrontmost lens group when the zoom lens barrel is retracted to aretracted position thereof.

[0008] It is desirable for the first lens frame to include an outer ringportion, an inner ring portion and a flange wall by which a front end ofthe outer ring portion and a front end of the inner ring portion areconnected, and the cam ring to be positioned between the outer ringportion and the inner ring portion.

[0009] It is desirable for the zoom lens barrel to include a second lensframe which is positioned inside the inner ring portion, and is guidedlinearly along the optical axis, wherein at least one opening, throughwhich the position of a lens group supported by the second lens frame inthe optical axis direction, can be adjusted is formed on the first lensframe.

[0010] It is desirable for the zoom lens barrel to include a biasingmember, positioned between the first lens frame and the light-shieldexterior ring, for biasing the light-shield exterior ring forwardrelative to the first lens frame.

[0011] It is desirable for the biasing device to be a compression coilspring.

[0012] The opening can include at least one outer opening formed on theouter ring portion, and at least one inner opening formed on the innerring portion. The outer opening and the inner opening are aligned in aradial direction of the zoom lens barrel.

[0013] It is desirable for the zoom lens barrel to include a stationarybarrel having a female helicoid formed on an inner peripheral surface ofthe stationary barrel. A male helicoid is formed on an outer peripheralsurface of the cam ring to be engaged with the female helicoid. A spurgear which is engaged with a drive pinion is formed on thread of themale helicoid.

[0014] It is desirable for the zoom lens barrel to include a second lensframe which is positioned inside the inner ring portion, is guidedlinearly along the optical axis, and includes a third cam follower; andan inner cam groove formed on an inner peripheral surface of the camring so that the third cam follower is engaged in the third cam groove.

[0015] It is desirable for the distance in the optical axis directionbetween said first cam groove and of said second cam groove changes froma predetermined position within a range before said zoom range

[0016] The present disclosure relates to subject matter contained inJapanese Patent Application No.2003-028631 (filed on Feb. 5, 2003) whichis expressly incorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be described below in detail withreference to the accompanying drawings in which:

[0018]FIG. 1 is a diagram showing reference moving paths of zoom lensgroups of a zoom lens system provided in an embodiment of a zoom lensbarrel according to the present invention;

[0019]FIG. 2 is an exploded perspective view in axial section of thezoom lens groups and lens support frames;

[0020]FIG. 3 is a longitudinal cross sectional view of the embodiment ofthe zoom lens barrel according to the present invention, showing anupper half of the zoom lens barrel from the optical axis thereof in aretracted state;

[0021]FIG. 4 is a view similar to that of FIG. 3, and shows an upperhalf of the zoom lens barrel from the optical axis thereof at thewide-angle extremity;

[0022]FIG. 5 is a view similar to that of FIG. 3, and shows a lower halfof the zoom lens barrel from the optical axis thereof at the telephotoextremity;

[0023]FIG. 6 is a transverse cross sectional view taken along VI-VI lineshown in FIG. 3;

[0024]FIG. 7 is a transverse cross sectional view taken along VII-VIIline shown in FIG. 3;

[0025]FIG. 8 is an exploded perspective view of a portion of the zoomlens barrel shown in FIG. 3;

[0026]FIG. 9 is an exploded perspective view of a portion of the zoomlens barrel shown in FIG. 3;

[0027]FIG. 10 is an exploded perspective view of a portion of the zoomlens barrel shown in FIG. 3, showing a first lens group moving ring andperipheral elements;

[0028]FIG. 11 is an exploded perspective view of a portion of the zoomlens barrel shown in FIG. 3, showing a third lens group moving ring andperipheral elements;

[0029]FIG. 12 is an exploded perspective view of a portion of the zoomlens barrel shown in FIG. 3, showing a second lens group moving ring andperipheral elements;

[0030]FIG. 13 is a longitudinal view of a portion of the zoom lensbarrel shown in FIG. 3, showing a portion of the second lens groupmoving ring and peripheral elements;

[0031]FIG. 14 is an exploded perspective view of a portion of the zoomlens barrel shown in FIG. 3, showing a stationary barrel, a pulse motorsupported by the stationary barrel, and peripheral elements, seen fromthe rear side thereof;

[0032]FIG. 15 is an exploded perspective view of a portion of the zoomlens barrel shown in FIG. 3, showing the stationary barrel, a fourthlens group and peripheral elements;

[0033]FIG. 16 is a developed view of a cam/helicoid ring, showing a setof first cam grooves of the cam/helicoid ring for moving the first lensgroup and a set of third cam grooves of the cam/helicoid ring for movingan exterior ring;

[0034]FIG. 17 is a developed view of the first lens group moving ring,the second lens group moving ring and the third lens group moving ring,showing linear guide mechanical linkages among the first through thirdlens group moving rings;

[0035]FIG. 18 is an enlarged view of a portion of the developed viewshown in FIG. 17; and

[0036]FIG. 19 is a developed view of the cam/helicoid ring, showing theshapes of a set of second cam grooves of the cam/helicoid ring formoving the second lens group.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0037] First of all, a zoom lens system (zoom lens optical system)provided in an embodiment of a zoom lens barrel of a camera according tothe present invention will be hereinafter discussed with reference toFIGS. 1 through 5. The zoom lens system of the zoom lens barrel 10 is avari-focal lens system consisting of four lens groups: a positive firstlens group L1, a negative second lens group L2, a positive third lensgroup L3 and a negative fourth lens group L4, in that order from theobject side (left side as viewed in FIG. 3). The first through thirdlens groups L1, L2 and L3 are moved relative to one another along anoptical axis O to vary the focal length of the zoom lens system and thefourth lens group L4 is moved along the optical axis O to make a slightfocus adjustment, i.e., to adjust a slight focus deviation caused by thevariation of the focal length. During the operation of varying the focallength of the zoom lens system between wide angle and telephoto, thefirst lens group L1 and the third lens group L3 move along the opticalaxis while maintaining the distance therebetween. The fourth lens groupL4 also serves as a focusing lens group. FIG. 1 shows both moving pathsof the first through fourth lens groups L1 through L4 during the zoomingoperation and moving paths for advancing/retracting operation. Bydefinition, a vari-focal lens is one whose focal point slightly varieswhen varying the focal length, and a zoom lens is one whose focal pointdoes not vary substantially when varying the focal length. However, thevari-focal lens system of the present invention is hereinafter referredto as a zoom lens system.

[0038] The overall structure of the zoom lens barrel 10 will behereinafter discussed with reference to FIGS. 1 through 19. The zoomlens barrel 10 is provided with a stationary barrel 11 which is fixed toa camera body (not shown). As shown in FIG. 8, the stationary barrel 11is provided on an inner peripheral surface thereof with a femalehelicoid 11 a and a set of three linear guide grooves 11 b which extendparallel to the optical axis O. The zoom lens barrel 10 is providedinside the stationary barrel 11 with a cam/helicoid ring (cam ring) 12.As shown in FIG. 9, the cam/helicoid ring 12 is provided, on an outerperipheral surface thereof in the vicinity of the rear end of thecam/helicoid ring 12, with a male helicoid 12 a which is engaged withthe female helicoid 11 a of the stationary barrel 11. The cam/helicoidring 12 is provided on the thread of the male helicoid 12 a with a spurgear 12 b which is always engaged with a drive pinion 13 (see FIG. 15).The drive pinion 13 is provided in a recessed portion 11 c (see FIG. 3)formed on an inner peripheral surface of the stationary barrel 11. Thedrive pinion 13 is supported by the stationary barrel 11 to be freelyrotatable in the recessed portion 11 c on an axis of the drive pinion13. Accordingly, forward and reverse rotations of the drive pinion 13cause the cam/helicoid ring 12 to move forward rearward along theoptical axis O while rotating about the optical axis O due to theengagement of the drive pinion 13 with the spur gear 12 b and theengagement of the female helicoid 11 a with the male helicoid 12 a. Inthe present embodiment of the zoom lens barrel 10, the cam/helicoid ring12 is the only element thereof which rotates about the optical axis O.

[0039] The zoom lens barrel 10 is provided around the cam/helicoid ring12 with a linear guide ring 14. The linear guide ring 14 is provided, onan outer peripheral surface thereof at the rear end of the linear guidering 14, with a set of three linear guide projections 14 a which projectradially outwards to be engaged in the set of three linear guide grooves11 b of the stationary barrel 11, respectively. The linear guide ring 14is provided, on an inner peripheral surface thereof at the rear end ofthe linear guide ring 14, with a set of three bayonet lugs 14 b (onlyone of them appears in FIGS. 1 through 4). The cam/helicoid ring 12 isprovided, on an outer peripheral surface thereof immediately in front ofthe male helicoid 12 a (the spur gear 12 b), with a circumferentialgroove 12 c in which the set of three bayonet lugs 14 b are engaged tobe rotatable about the optical axis O in the circumferential groove 12c. Accordingly, the linear guide ring 14 is linearly movable along theoptical axis O together with the cam/helicoid ring 12 without rotatingabout the optical axis O.

[0040] The zoom lens barrel 10 is provided around the cam/helicoid ring12 with a first lens group moving ring (first lens frame) 15 whichsupports the first lens group L1, and is further provided around thefirst lens group moving ring 15 with an exterior ring 16 serving as alight shield member (light-shield exterior ring). The zoom lens barrel10 is provided inside the cam/helicoid ring 12 with a second lens groupmoving ring (second lens frame) 17 which supports the second lens groupL2. As shown in FIGS. 4, 9 and 16, the cam/helicoid ring 12 is providedon an outer peripheral surface thereof with a set of three first camgrooves (first outer cam grooves) C15 for moving the first lens groupmoving ring 15 and a set of three third cam grooves (second outer camgrooves) C16 for moving the exterior ring 16, and is further provided onan inner peripheral surface of the cam/helicoid ring 12 with a set ofsix second cam grooves (inner cam grooves) C17 for moving the secondlens group moving ring 17 (see FIG. 19). The set of three first camgrooves C15 and the set of three third cam grooves C16 are slightlydifferent in shape, and are apart from one another at predeterminedintervals in a circumferential direction of the cam/helicoid ring 12.The set of six second cam grooves C17 have the same basic cam diagrams,and includes three front second cam grooves C17, and three rear secondcam grooves C17 which are positioned behind the three front second camgrooves C17 in the optical axis direction (vertical direction as viewedin FIG. 19), respectively; the three front second cam grooves C17 areapart from one another in a circumferential direction of thecam/helicoid ring 12 while the three rear second cam grooves C17 areapart from one another in a circumferential direction of thecam/helicoid ring 12. Each of the first lens group moving ring 15, theexterior ring 16 and the second lens group moving ring 17 is linearlyguided along the optical axis O. A rotation of the cam/helicoid ring 12causes the first lens group moving ring 15, the exterior ring 16 and thesecond lens group moving ring 17 to move along the optical axis O inaccordance with the contours of the set of three first cam grooves C15,the set of three third cam grooves C16 and the set of six second camgrooves C17, respectively.

[0041] Linear guide mechanical linkages among the first lens groupmoving ring 15, the exterior ring 16 and the second lens group movingring 17 will be discussed hereinafter. As shown in FIGS. 4 and 5, thefirst lens group moving ring 15 is provided with an outer ring portion15X, an inner ring portion 15Y and a flange wall 15Z by which the frontend of the outer ring portion 15X and the front end of the inner ringportion 15Y are connected to have a substantially U-shaped crosssection. The cam/helicoid ring 12 is positioned between the outer ringportion 15X and the inner ring portion 15Y. Three cam followers 15awhich are respectively engaged in the set of three first cam grooves C15are fixed to the outer ring portion 15X in the vicinity of the rear endthereof. The zoom lens barrel 10 is provided with a first lens groupsupport frame 24 which supports the first lens group L1. As shown inFIGS. 8 and 9, the first lens group support frame 24 is fixed to theinner ring portion 15Y at the front end thereof through a male threadportion and a female thread portion which are formed on an outerperipheral surface of the first lens group support frame 24 and an innerperipheral surface of the inner ring portion 15Y, respectively (see FIG.10). The first lens group support frame 24 can be rotated relative tothe first lens group moving ring 15 to adjust the position of the firstlens group support frame 24 along the optical axis O relative to thefirst lens group moving ring 15 to carry out a zooming adjustment (whichis an adjustment operation which is carried out in a manufacturingprocess of the zoom lens barrel if necessary).

[0042] The linear guide ring 14, which is linearly guided along theoptical axis O by the stationary barrel 11, is provided, on an innerperipheral surface thereof at approximately equi-angular intervals(intervals of approximately 120 degrees), with a set of three linearguide grooves 14 c (only one of them appears in FIG. 9), while the outerring portion 15X of the first lens group moving ring 15 is provided atthe rear end thereof with a set of three linear guide projections 15 b(see FIG. 10) which project radially outwards to be engaged in the setof three linear guide grooves 14 c, respectively. The outer ring portion15X is provided with a set of three assembly slots 15 c (see FIGS. 10and 16), and is further provided at the rear ends of the set of threeassembly slots 15 c with a set of linear guide slots 15 d which arecommunicatively connected with the set of three assembly slots 15 c andare smaller in width than the set of three assembly slots 15 c,respectively. Three linear guide keys 16 a which are fixed to theexterior ring 16 which is positioned between the outer ring portion 15Xand the linear guide ring 14 are engaged in the set of linear guideslots 15 d, respectively. The maximum relative moving distance betweenthe first lens group moving ring 15 and the exterior ring 16 along theoptical axis O (the difference in shape between the set of three firstcam grooves C15 and the set of three third cam grooves C16) is only aslight distance, and the length of each linear guide slot 15 d in theoptical axis direction is correspondingly short. A set of three camfollowers 16 b which are engaged in the set of three third cam groovesC16 are fixed to the set of three linear guide keys 16 a, respectively(see FIGS. 7 and 9).

[0043] The zoom lens barrel 10 is provided between the first lens groupmoving ring 15 and the exterior ring 16 with a compression coil spring19 (see FIGS. 3 through 5). The compression coil spring 19 biases thefirst lens group moving ring 15 rearward to remove backlash between theset of three first cam grooves C15 and the set of three cam followers 15a, and at the same time, biases the exterior ring 16 forward to removebacklash between the set of three third cam grooves C16 and the set ofthree cam followers 16 b.

[0044] As shown in FIG. 16, the set of three first cam grooves C15 andthe set of three third cam grooves C16 are shaped slightly differentfrom each other in their respective retracting positions, as comparedwith their respective photographing ranges (zooming ranges), so that theexterior ring 16 advances from the photographing position thereofrelative to the first lens group moving ring 15 to prevent barrierblades of a lens barrier unit 30 (see FIG. 8) and the first lens groupL1 from interfering with each other when the zoom lens barrel 10 isfully retracted as shown in FIG. 3. More specifically, as shown in FIG.16, the shapes of the first cam grooves C15 and the third cam groovesC16 are determined so that the distance Q in the optical axis directionbetween the first cam grooves C15 and the third cam grooves C16 in thepreparation ranges (i.e., the range between the retracted position andthe position at which the lens barrier unit 30 is fully open) is longerthan that of the zoom ranges (i.e., the range between the wide-angleextremity and the telephoto extremity). Namely, throughout the entiretyof the preparation ranges the distance Q=Q1, however, the distance Qgradually reduces from a position OP2 at a predetermined distance from afully opened position OP1 of the lens barrier unit 30 (i.e., from aposition whereby the first lens group L1 and the lens barrier unit 30 donot interfere with each other), so that the distance Q=Q2 (<Q1) at thewide-angle extremity, and the distance Q=Q2 in the entirety of the zoomranges.

[0045] It can be seen in FIG. 3 that a clearance cl between the flangewall 15Z of the first lens group moving ring 15 and a flange wall 16f ofthe exterior ring 16 when the zoom lens barrel 10 is in the retractedposition is greater than that when the zoom lens barrel 10 is in aready-to-photograph position as shown in FIG. 4 or 5. In other words,when the zoom lens barrel 10 is in a ready-to-photograph position asshown in FIG. 4 or 5, the flange wall 15Z of the first lens group movingring 15 and the flange wall 16f of the exterior ring 16 are positionedclosely to each other to reduce the length of the zoom lens barrel 10.The lens barrier unit 30 is supported by the exterior ring 16 at thefront end thereof. The zoom lens barrel 10 is provided, immediatelybehind the lens barrier unit 30 (between the lens barrier unit 30 andthe flange wall 16f of the exterior ring 16), with a barrieropening/closing ring 31 (see FIG. 9). Rotating the barrieropening/closing ring 31 at the retracted position via rotation of thecam/helicoid ring 12 causes the barrier blades of the lens barrier unit30 to open and shut. The mechanism for opening and closing the barrierblades using a barrier opening/closing ring such as the barrieropening/closing ring 31 is known in the art.

[0046] Note that in the illustrated embodiment, although the shapes ofthe first cam grooves C15 and the third cam grooves C16 are determinedso that the distance Q (i.e., Q2) is constant (unchanging) over theentire zoom range, the distance Q (i.e., Q2) can be determined so as tochange in accordance with the focal length. Furthermore, the distance Q2over the zoom range can be determined so as to be greater than thedistance Q1 over the preparation range.

[0047] The front end of each third cam groove C16 is open on a front endsurface of the cam/helicoid ring 12 to be formed as an open end C16 a(see FIG. 16) through which the associated cam follower 16 b of theexterior ring 16 is inserted into the third cam groove C16. Likewise,the front end of each first cam groove C15 is open on a front endsurface of the cam/helicoid ring 12 to be formed as an open end C15 a(see FIG. 16) through which the associated cam follower 15 a of thefirst lens group moving ring 15 is inserted into the first cam grooveC15.

[0048] The inner ring portion 15Y of the first lens group moving ring 15is provided on an inner peripheral surface thereof with a set of threelinear guide projections 15 f which are elongated in a directionparallel to the optical axis O, while the second lens group moving ring17 is provided with a set of three linear guide slots (linear guidethrough-slots) 17 a which are elongated in a direction parallel to theoptical axis O to be engaged with the set of three linear guideprojections 15 f to be freely slidable relative thereto along theoptical axis 0 (see FIGS. 6, 7 and 17). Each linear guide projection 15f is provided along a substantially center thereof with a hanging groove15 e which is elongated in a direction parallel to the optical axis Oand which has a substantially T-shaped cross section as shown in FIG. 6.The three linear guide projections 15 f and the three linear guide slots17 a constitute a first linear guide mechanism. The rear end of eachhanging groove 15 e is closed (see FIGS. 17 and 18). The second lensgroup moving ring 17 is provided on an outer peripheral surface thereofwith six cam followers 17 c which are engaged in the set of six secondcam grooves C17 of the cam/helicoid ring 12, respectively.

[0049] The zoom lens barrel 10 is provided inside the second lens groupmoving ring 17 with a third lens group moving ring (third lens frame) 18which supports the third lens group L3. The third lens group moving ring18 is provided on an outer peripheral surface thereof with a set ofthree linear guide projections 18 a which are elongated in a directionparallel to the optical axis O to be engaged in the set of three linearguide slots 17 a of the second lens group moving ring 17 to be freelyslidable relative thereto along the optical axis O, respectively. Thethird lens group moving ring 18 is provided on a center of each linearguide projection 18 a at the front end thereof with a linear moving key(stop projection) 18 b (see FIGS. 11, 17 and 18) which has asubstantially T-shaped cross section to be engaged in the associatedhanging groove 15 e. The three linear guide projections 15 f, the threehanging groove 15 e and the three linear moving keys 18 b constitute asecond linear guide mechanism. Furthermore, the three linear guide slots17 a and the three linear guide projections 18 a constitute a thirdlinear guide mechanism. As shown in FIG. 11, the zoom lens barrel 10 isprovided with a shutter unit 20 which is inserted into the third lensgroup moving ring 18 to be positioned in front of the third lens groupL3. The shutter unit 20 is fixed to the third lens group moving ring 18by a fixing ring 20 a. The zoom lens barrel 10 is provided between thethird lens group moving ring 18 (the fixing ring 20 a) and the secondlens group moving ring 17 with a compression coil spring 21 whichcontinuously biases the third lens group moving ring 18 rearwardsrelative to the second lens group moving ring 17. The rear limit of thisrearward movement of the third lens group moving ring 18 relative to thesecond lens group moving ring 17 is determined by the three linearmoving keys 18 b contacting the closed rear ends of the three hanginggrooves 15 e, respectively. Namely, when the zoom lens barrel 10 is in aready-to-photograph position, each linear moving key 18 b remains incontact with the rear end of the associated hanging groove 15 e of thefirst lens group moving ring 15 to keep the distance between the firstlens group L1 and the third lens group L3 constant. When the zoom lensbarrel 10 changes from a ready-to-photograph state to the retractedstate shown in FIG. 3, a further rearward movement of the first lensgroup L1 in accordance with contours of the set of three first camgrooves C15, after the third lens group L3 (the third lens group movingring 18) has reached the mechanical rear moving limit thereof, causesthe first lens group L1 to approach the third lens group L3 whilecompressing the compression coil spring 21 (see FIG. 1). Each linearmoving key 18 b is formed so that the radially outer end thereof bulgesto be prevented from coming off the associated hanging groove 15 e.

[0050] Although a biasing force of the compression coil spring 21 can beapplied directly to the second lens group moving ring 17 (i.e., althoughthe second lens group L2 can be fixed to the second lens group movingring 17), the second lens group L2 is made to be capable of movingrearward relative to the second lens group moving ring 17 for thepurpose of further reduction in length of the zoom lens barrel 10 in theretracted state thereof in the present embodiment of the zoom lensbarrel. FIGS. 12 and 13 show this structure for the further reduction inlength of the zoom lens barrel 10. The second lens group moving ring 17is provided at the front end thereof with a cylindrical portion 17 ehaving an inner flange 17 d. Three linear guide grooves 17 f, whichextend parallel to the optical axis direction and open at the front andrear ends thereof, are formed at equi-angular intervals on thecylindrical portion 17 e. The zoom lens barrel 10 is provided inside thesecond lens group moving ring 17 with an intermediate ring 25. Theintermediate ring 25 is provided at the front end thereof with a flangeportion 25 a which is fitted in the cylindrical portion 17 e to befreely slidable on the cylindrical portion 17 e in the optical axisdirection. Three guide projections 25 d which radially extend outwardsare provided on the outer peripheral surface of the flange-portion 25 a.The three guide projection 25 d are respectively engaged with the threelinear guide grooves 17 f of the second lens group moving ring 17 fromthe rear side of the second lens group moving ring 17. Accordingly, theintermediate ring 25 is prevented from rotating about the optical axiswith respect to the second lens group moving ring 17, and can onlyrelatively move in the optical axis direction. The front face of theflange portion 25 a can move forwards until sliding contact is made withthe rear face of the inner flange 17 d. The zoom lens barrel L2 isprovided inside the second lens group moving ring 17 with a second lensgroup support frame 26 to which the second lens group L2 is fixed. Amale thread 26 b of the second lens group support frame 26 is screwedinto female thread 25 e formed on the inner periphery of theintermediate ring 25. Accordingly, the position of the second lens groupL2 relative to the intermediate ring 25 which is prevented from rotatingabout the optical axis can be adjusted in the optical axis direction(zooming adjustment) by rotating the second lens group support frame 26relative to the intermediate ring 25. After this adjustment, the secondlens group support frame 26 can be permanently fixed to the intermediatering 25 by putting drops of an adhesive agent into a radial through hole25 b formed on the intermediate ring 25. The second lens group supportframe 26 is provided on an outer peripheral surface thereof with anouter flange 26 a, and a clearance C2 (see FIG. 13) for the zoomingadjustment exits between a front end surface of the inner flange 17 dand the outer flange 26 a. The compression coil spring 21 biases theintermediate ring 25 forward, and the intermediate ring 25 is held at aposition where the flange portion 25 a contacts with the inner flange 17d when the zoom lens barrel 10 is in a ready-to-photograph state.Namely, on the one hand, the position of the second lens group L2 iscontrolled by the set of six second cam grooves C17 when the zoom lensbarrel 10 is in a ready-to-photograph state; on the other hand, thesecond lens group support frame 26 is pushed rearward mechanically bythe rear end of the first lens group support frame 24 to thereby movethe outer flange 26 a of the second lens group support frame 26 rearwardto a point where the outer flange 26 a contacts with the inner flange 17d when the zoom lens barrel 10 is retracted to the retracted positionthereof. This reduces the length of the zoom lens barrel 10 by a lengthcorresponding to the clearance C2.

[0051] The zoom lens barrel 10 is provided immediately behind theintermediate ring 25 with a light shield ring 27 which is supported bythe intermediate ring 25. As shown in FIG. 12, the light shield ring 27is provided with a ring portion 27 a and a set of three leg portions 27b which extend forward from the ring portion 27 a at intervals ofapproximately 120 degrees. Each leg portion 27 b is provided at thefront end thereof with a hook portion 27 c which is formed by bendingthe tip of the leg portion 27 b radially outwards. The intermediate ring25 is provided on an outer peripheral surface thereof with a set ofthree engaging holes 25 c with which the hook portions 27 c of the setof three leg portions 27 b are engaged, respectively (see FIG. 12). Thezoom lens barrel 10 is provided between the light shield ring 27 and thesecond lens group support frame 26 with a compression coil spring 28having a substantially truncated conical shape which continuously biasesthe light shield ring 27 rearwards. When the zoom lens barrel 10 isretracted toward the retracted position, the light shield ring 27approaches the second lens group support frame 26 while compressing thecompression coil spring 28 after reaching the rear moving limit of thelight shield ring 27. The lengths of the set of three engaging holes 25c in the optical axis direction are determined to allow the ring portion27 a to come into contact with the second lens group support frame 26.

[0052] The compression coil spring 28 also serves as a device forremoving backlash between the intermediate ring 25 and the second lensgroup support frame 26 when the second lens group support frame 26 isrotated relative to the intermediate ring 25 for the aforementionedzooming adjustment. The zooming adjustment is performed by rotating thesecond lens group support frame 26 relative to the intermediate ring 25to adjust the position of the second lens group L2 in the optical axisdirection relative to the intermediate ring 25 while viewing theposition of an object image. This zooming adjustment can be performedwith precision with backlash between the intermediate ring 25 and thesecond lens group support frame 26 being removed by the compression coilspring 28.

[0053] The zoom lens barrel 10 is provided behind the third lens groupmoving ring 18 with a fourth lens group support frame 22 to which thefourth lens group L4 is fixed. As described above, the fourth lens groupL4 is moved to make a slight focus adjustment to the vari-focal lenssystem to adjust a slight focal deviation thereof while the firstthrough third lens groups L1, L2 and L3 are moved relative to oneanother to vary the focal length of the zoom lens system, and is alsomoved as a focusing lens group. The fourth lens group L4 is moved alongthe optical axis O by rotation of a pulse motor 23 (see FIGS. 5 and 14).The pulse motor 23 is provided with a rotary screw shaft 23 a. A nutmember 23 b is screwed on the rotary screw shaft 23 a to be preventedfrom rotating relative to the stationary barrel 11. The nut member 23 bis continuously biased by an extension coil spring S in a direction tocontact with a leg portion 22 a which projects radially outwards fromthe fourth lens group support frame 22 (see FIGS. 5 and 15). The fourthlens group support frame 22 is prevented from rotating by guide bars 22b, which extend in direction parallel to the optical axis direction,which are slidably engaged with radial projecting followers 22 c whichextend radially outwards from the fourth lens group support frame 22(see FIGS. 2 and 15). Accordingly, rotations of the pulse motor 23forward and reverse cause the fourth lens group support frame 22 (thefourth lens group L4) to move forward and rearward along the opticalaxis O, respectively. Rotations of the pulse motor 23 are controlled inaccordance with information on focal length and/or information on objectdistance.

[0054] Accordingly, in the above described embodiment of the zoom lensbarrel, rotating the cam/helicoid ring 12 by rotation of the drivepinion 13 causes the first lens group moving ring 15, the exterior ring16 and the second lens group moving ring 17 to move along the opticalaxis O in accordance with contours of the set of three first cam groovesC15, the set of three third cam grooves C16 and the set of six secondcam grooves C17, respectively. When the first lens group moving ring 15moves forward from the retracted position, firstly the three linearmoving keys 18 b contact the rear ends of the three hanging grooves 15e, respectively, and subsequently the third lens group moving ring 18moves together with the first lens group moving ring 15 with the threelinear moving key 18 b remaining in contact with the rear ends of thethree hanging grooves 15 e, respectively. The position of the fourthlens group L4 is controlled by the pulse motor 23, whose rotations arecontrolled in accordance with information on focal length, to make aslight focus adjustment to the vari-focal lens system to adjust a slightfocal deviation thereof. As a result, reference moving paths as shown inFIG. 1 for performing a zooming operation are obtained. Rotations of thepulse motor 23 are also controlled in accordance with information onobject distance to perform a focusing operation.

[0055] As described above, in the present embodiment of the zoom lensbarrel 10, the first lens group moving ring (first lens frame) 15, whichsupports the first lens group L1, and the exterior ring (light-shieldexterior ring) 16 are positioned around the cam/helicoid ring (cam ring)12 which is driven to rotate by rotation of the drive pinion 13. Thefirst lens group moving ring 15 includes the outer ring portion 15X,which is positioned around the cam/helicoid ring 12, the inner ringportion 15Y, which is positioned inside the cam/helicoid ring 12, andthe flange wall 15Z, by which the front end of the outer ring portion15X and the front end of the inner ring portion 15Y are connected. Thecompression coil spring (biasing device) 19 is positioned in acompressed fashion between the first lens group moving ring 15 and theexterior ring 16. The three followers 15 a of the first lens groupmoving ring 15 are respectively engaged in the set of three first camgrooves (first outer cam grooves) C15 that are formed on an outerperipheral surface of the cam/helicoid ring 12, and the first lens groupmoving ring 15 is linearly guided along the optical axis O by the linearguide ring 14. The set of three linear guide keys 16 a of the exteriorring 16 are respectively engaged in the set of three linear guide slots15 d of the first lens group moving ring 15, the set of three camfollowers 16 b of the exterior ring 16 are respectively engaged in theset of three third cam grooves (second outer cam grooves) C16 that areformed on an outer peripheral surface of the exterior ring 16, and theexterior ring 16 is linearly guided along the optical axis O by thefirst lens group moving ring 15. Since the set of three first camgrooves C15 and the set of three third cam grooves C16 have the sameshape and size in their respective photographing ranges (i.e., theirrespective zooming ranges between wide angle extremity and telephotoextremity) as shown in FIG. 16, the exterior ring 16 moves in accordancewith the same moving path as the first lens group moving ring 15 alongthe optical axis O to protect the first lens group moving ring 15 whilereinforcing the strength of the first lens group moving ring 15.Moreover, it is sufficient to provide the first lens group moving ring15 with only the set of linear guide slots 15 d, each of which has arelative short length, as a mechanism for guiding the exterior ring 16linearly along the optical axis O. This makes a further reduction inlength of the zoom lens barrel 10 possible.

[0056] The set of three first cam grooves C15 and the set of three thirdcam grooves C16 have different shapes in their respective retractingranges so that the exterior ring 16 advances from the photographingposition thereof relative to the first lens group moving ring 15 toprevent the barrier blades of the lens barrier unit 30 from interferingwith the first lens group L1.

[0057] Additionally, a set of three outer openings 15X1 for the zoomingadjustment and a set of three inner openings 15Y1 for the zoomingadjustment which are aligned in radial directions of the zoom lensbarrel 10 are formed on the outer ring portion 15X and the inner ringportion 15Y, respectively (see FIGS. 4, 8, 10 and 16). Before theexterior ring 16 is mounted to the cam/helicoid ring 12 (before an outerperipheral surface of the first lens group moving ring 15 is coveredwith the exterior ring 16), it is possible to carry out theaforementioned zooming adjustment (for adjusting the position of thesecond lens group L2 relative to the intermediate ring 25 along theoptical axis O) by firstly moving the first lens group moving ring 15and the second lens group moving ring 17 to their respective wide-angleextremity positions (the positions shown in FIG. 4), and subsequentlyrotating the second lens group support frame 26 relative to theintermediate ring 25 with a special jig (not shown) which can be engagedwith the second lens group support frame 26 from the outside of thefirst lens group moving ring 15 through the set of three outer openingthree outer openings 15X1 and the set of three inner openings 15Y1.After this zooming adjustment is completed, the second lens groupsupport frame 26 can be permanently fixed to the intermediate ring 25 byputting drops of an adhesive agent into the radial through hole 25 b ofthe intermediate ring 25.

[0058] As described above, the exterior ring 16 of the presentembodiment of the zoom lens barrel 10 not only shields the set of threeouter openings 15X1 and the set of three inner openings 15Y1 of thefirst lens group moving ring 15 in a light-tight fashion but alsoremoves backlash of the first lens group moving ring 15 (backlashbetween the set of three first cam grooves C15 and the set of threefollowers 15 c), supports the lens barrier unit 30, and prevents thebarrier blades of the lens barrier unit 30 and the first lens group L1from interfering with each other by advancing the exterior ring 16 fromthe photographing position thereof relative to the first lens groupmoving ring 15 when the zoom lens barrel 10 is retracted to theretracted position. Accordingly, the exterior ring 16 ismulti-functional.

[0059] The above described structure of the zoom lens barrel which makesthe exterior ring 16 multi-functional can be applied to any zoom lensbarrel including a cam ring and a lens support ring, regardless ofwhether the cam ring includes a helicoid such as the male helicoid 12 aof the cam/helicoid ring 12.

[0060] As can be understood from the foregoing, according to the presentinvention, a light-shield exterior ring, which formerly serves only as alight shield member, can be made to serve as a multi-functional member.

[0061] Obvious changes may be made in the specific embodiment of thepresent invention described herein, such modifications being within thespirit and scope of the invention claimed. It is indicated that allmatter contained herein is illustrative and does not limit the scope ofthe present invention.

What is claimed is:
 1. A zoom lens barrel comprising: a cam ring whichis driven to rotate; a first lens frame which is positioned around saidcam ring to be guided linearly along an optical axis, said first lensframe supporting a frontmost lens group of a zoom lens system,; alight-shield exterior ring which is positioned around said first lensframe; a first outer cam groove and a second outer cam groove which areformed on an outer peripheral surface of said cam ring, each said firstand second cam grooves including a zooming range for performing azooming operation of said zoom lens system; and a first cam followerformed on said first lens frame, said first cam follower being engagedin said first outer cam groove; a second cam follower formed on saidlight-shield exterior ring, said second cam follower being engaged insaid second outer cam groove through a linear guide slot which iselongated in a direction parallel to said optical axis, which is formedon said first lens frame, and wherein said first outer cam groove andsaid second outer cam groove are shaped so as to move said first lensframe and said light-shield exterior ring in the same moving path insaid zooming ranges thereof.
 2. The zoom lens barrel according to claim1, further comprising a lens barrier unit including at least one barrierblade, wherein said lens barrier unit is supported by said light-shieldexterior ring at a front end thereof, and wherein retracting ranges ofsaid first outer cam groove and said second outer cam groove are shapedso that said light-shield exterior ring advances from a photographingposition thereof relative to said first lens frame to position said lensbarrier unit in front of said frontmost lens group without the lensbarrier unit interfering with said frontmost lens group when said zoomlens barrel is retracted to a retracted position thereof.
 3. The zoomlens barrel according to claim 1, wherein said first lens framecomprises an outer ring portion, an inner ring portion and a flange wallby which a front end of said outer ring portion and a front end of saidinner ring portion are connected, and wherein said cam ring ispositioned between said outer ring portion and said inner ring portion.4. The zoom lens barrel according to claim 3, further comprising asecond lens frame which is positioned inside said inner ring portion,and is guided linearly along said optical axis, wherein at least oneopening, through which the position of a lens group supported by saidsecond lens frame in said optical axis direction, can be adjusted isformed on said first lens frame.
 5. The zoom lens barrel according toclaim 1, further comprising a biasing member, positioned between saidfirst lens frame and said light-shield exterior ring, for biasing saidlight-shield exterior ring forward relative to said first lens frame. 6.The zoom lens barrel according to claim 5, wherein said biasing devicecomprises a compression coil spring.
 7. The zoom lens barrel accordingto claim 4, wherein said opening comprises: at least one outer openingformed on said outer ring portion, and at least one inner opening formedon said inner ring portion, wherein said outer opening and said inneropening are aligned in a radial direction of said zoom lens barrel. 8.The zoom lens barrel according to claim 1, further comprising astationary barrel having a female helicoid formed on an inner peripheralsurface of said stationary barrel, wherein a male helicoid is formed onan outer peripheral surface of said cam ring to be engaged with saidfemale helicoid, and wherein a spur gear which is engaged with a drivepinion is formed on thread of said male helicoid.
 9. The zoom lensbarrel according to claim 1, further comprising: a second lens framewhich is positioned inside said inner ring portion, is guided linearlyalong said optical axis, and includes a third cam follower; and an innercam groove formed on an inner peripheral surface of said cam ring sothat said third cam follower is engaged in said third cam groove. 10.The zoom lens barrel according to claim 2, wherein the distance in theoptical axis direction between said first cam groove and of said secondcam groove changes from a predetermined position within a range beforesaid zoom range.